Pressure Balance System for Top Mount Pulser

ABSTRACT

For balancing pressure in a downhole tool between a first section filled with hydraulic fluid and a second section filled with drilling fluid, a system utilizes a sleeve located inside a housing of the downhole tool, a piston located inside the sleeve. A stem traverses the piston through a hole in the piston. The stem is used to couple a solenoid to a valve system of the downhole tool, for example. The piston is sized to control a wobble of the piston and to allow reciprocation of the piston inside the sleeve. The hole in the piston is sized to control a wobble of the stem and to allow reciprocation of the stem through the hole in the piston.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. provisional application Ser. No. 63/031,389, filed on May 28, 2020, incorporated herein by reference for all and any purposes.

BACKGROUND

This disclosure relates generally to methods and apparatus for balancing pressure in a downhole tool between a first section filled with hydraulic fluid and a second section filled with drilling fluid.

Measurement While Drilling (“MWD”) tool strings are used in the oil and gas industry to help the driller locate and guide the drill bit as it cuts into the earth. An MWD tool string includes sensors that are usually encapsulated inside metal housings that can withstand drilling and harsh downhole conditions. An example MWD tool string may comprise the following tools: a mud pulse telemetry tool, directional sensors such as magnetometers, inclinometers, or gyroscopes, batteries, and formation evaluation sensors such as a natural gamma-ray sensor. The sensor measurements obtained from the directional sensors and/or formation evaluation sensors are communicated up to the earth's surface using the mud pulse telemetry tool so that the driller receives quasi-real-time data about the orientation of the tool string and the nature of the formation being drilled.

FIG. 1 illustrates a known mud pulse telemetry tool 10. The tool 10 can be located at the top of an MWD tool string inside of a drill pipe (not shown). Drilling fluid 14 is pumped down the drill pipe through the tool 10 and down the rest of the drill pipe. Data from sensors located in the MWD tool string are encoded into pressure oscillations, which the mud pulse telemetry tool 10 can generate.

The tool 10 controllably varies a variable (e.g., on and off) restriction of fluid flow, which creates a pressure oscillation in the drilling fluid 14. The pressure oscillation propagates in the drill pipe and up to the earth's surface. In the tool 10, the variable restriction of fluid flow is provided by displacing a poppet 28 relative to an orifice 38. For example, as the poppet 28 moves up toward the orifice 38, it restricts the flow of drilling fluid that is being pumped down the drill pipe. This flow restriction creates an increase in pressure inside the drill pipe. As the poppet 28 moves down away from the orifice 38, it frees the flow of drilling fluid that is being pumped down the drill pipe. This flow easement creates a decrease in pressure inside the drill pipe. Then, the pressure oscillations inside the drill pipe are measured using pressure sensors located at the surface of the well. The pressure oscillations inside the drill pipe are decoded using software to recover the data from the sensors located in the MWD tool string in quasi-real-time.

In order to move the poppet 28 relative to the orifice 38, the poppet 28 is coupled to a shaft 20, which in turn is coupled to a main piston 26. Thus, the main piston 26 moves the poppet 28. The main piston 26 moves up and down depending on the differential of drilling fluid pressure between its top face 18 and its bottom face 19. The top face 18 of the piston 26 is exposed to drilling fluid that has flown downstream of the poppet 28 and orifice 38. The bottom face 19 of the piston 26 is selectively exposed to higher-pressure drilling fluid or lower-pressure drilling fluid.

For this selection to be made, a mechanical/electrical mechanism is provided to pilot a spring-loaded valve system that includes a bottom valve 22 and a top valve 30. The mechanical/electrical mechanism also includes a low-power electric solenoid (not shown) that is used to operate the valve system. The valve system either directs drilling fluid flowing from high-pressure inlet 16 that extends through a central bore in the shaft 20 toward the bottom face 19 of the piston 26, or directs drilling fluid from the bottom face 19 of the piston 26 toward low-pressure outlet 32. For example, the bottom valve 22 and top valve 30 may move up and down in unison in the valve system. When the bottom valve 22 and top valve 30 are in an upper end of course position, the bottom valve 22 may isolate a passageway 24 from the low-pressure outlet 32 while the top valve 30 simultaneously opens the passageway 24 to the high-pressure inlet 16. Conversely, when the bottom valve 22 and top valve 30 are in a lower end of course position, the bottom valve 22 may open the passageway 24 to the low-pressure outlet 32 while the top valve 30 simultaneously isolates the passageway 24 from high-pressure inlet 16.

The valve system is in direct contact with the drilling fluid and operates at the pressure in the well encountered in downhole conditions. In order to alleviate the effects of downhole pressure, a pressure balance system 40 is used to equalize pressure so that the solenoid does not need to overcome the downhole pressure and is able to operate the valve system. With the pressure balance system 40, the solenoid can achieve the opening and closing of the valve system without requiring excessive electrical power.

FIG. 2 illustrates a known pressure balance system 40. The pressure balance system 40 includes a piston 44, a cylindrical sleeve 42, a cap 48, a cylindrical stem 36 (shown in FIG. 1), and a piston stop 39 (shown in FIG. 1), all of which located inside a pressure housing 34 (shown in FIG. 1). The piston 44 is positioned inside of the sleeve 42, where it can reciprocate. A space between the outer diameter of the piston 44 and the inner diameter of the sleeve 42 is sealed using an O-ring 46. The piston 44 has a center hole traversed by the stem 36. The stem 36 can reciprocate in the center hole. A space between the outer diameter of the stem 36 and the inner diameter of the piston 44 is sealed using a quad seal 56, the illustration of which is schematized. The cap 48 is located at the bottom end of the sleeve 42. The cap 48 and O-rings 50 are used to create a seal between the sleeve 42 and pressure housing 34. The piston stop 39 is used to stop the piston 44 from coming out of the sleeve 42. The piston stop 39 may preferably have a rectangular cross-section, such as illustrated in FIG. 3. The piston 44 is designed to be exposed to drilling fluid on the upper side, and hydraulic fluid on the lower side. The O-Rings 46, 50, and the quad seal 56 are used to isolate the drilling fluid and the hydraulic fluid from each other.

The solenoid that is used to operate the valve system contacts the lower end of the stem 36 on the side of the piston 44 immersed in hydraulic fluid, and the valve system contacts the stem 36 on the side of the piston 44 immersed in the drilling fluid. When the solenoid is powered on and off, the stem 36 moves up and down within the pressure balance system 40.

When the upper side of the piston 44 is exposed to drilling fluid, the force generated by the pressure applied to that side of the piston 44 causes the piston to move downward towards a chamber filled with hydraulic fluid. The piston 44 compresses the hydraulic fluid, which, in turn, creates an equal and opposite force in the direction towards the drilling fluid. As the tool 10 operates in the well, the piston 44 adjusts its position as the downhole pressure conditions change along the well. With the pressure across the piston 44 balanced, the solenoid can then easily move the stem 36 up and down. Thus, the pressure balance system 40 allows utilizing a solenoid in the tool 10 in an energy-efficient way despite the tool 10 being immersed in drilling fluid and exposed to drilling and harsh downhole conditions. In contrast, without the pressure balance system 40, the solenoid may not be able to overcome the high forces generated by the pressure of the drilling fluid applied to the stem 36, and may not be able to move the stem 36 and the valve system up and down.

Furthermore, the piston 44 also adjusts its position as the downhole temperature conditions change. Temperature changes cause the hydraulic fluid to expand or condense. The piston 44 moves within the sleeve 42 as the hydraulic fluid expands or condenses.

However, despite these advances, the drilling fluid can sometimes invade the chamber filled with hydraulic fluid. The drilling fluid may have a thermal expansion coefficient and a compressibility that not suitable for the predetermined course of the piston 44 in the sleeve 42. This may cause the piston 44 to abut the piston stop 39. When this abutment occurs, the pressure balance system 40 may no longer be able to properly balance pressure. As a result, the solenoid may no longer have sufficient electrical power to move the stem 36 and the valve system up and down, leading to the tool 10 not being able to provide mud pulse telemetry.

Thus, there is a continuing need in the art for methods and apparatus for a pressure balance system. Preferably, the pressure balance system is less prone to invasion of the chamber filled with hydraulic fluid by the drilling fluid.

BRIEF SUMMARY OF THE DISCLOSURE

The disclosure describes a system, which may be used for balancing pressure in a downhole tool between a first section filled with hydraulic fluid and a second section filled with drilling fluid.

The system may comprise a sleeve that is located inside a housing of the downhole tool.

The system may comprise a piston that is located inside the sleeve. The piston may have one side exposed to the hydraulic fluid and another, opposite side exposed to the drilling fluid. The piston may have an outer surface adjacent to an inner surface of the sleeve. The outer surface of the piston may be sized to control a wobble of the piston along a direction perpendicular to a longitudinal axis of the piston. The outer surface of the piston may further be sized to allow reciprocation of the piston inside the sleeve.

The system may comprise a stem that is traversing the piston.

Furthermore, the disclosure describes another system, which may also be used for balancing pressure in a downhole tool between a first section filled with hydraulic fluid and a second section filled with drilling fluid.

The system may comprise a sleeve that is located inside a housing of the downhole tool.

The system may comprise a piston that is located inside the sleeve. The piston may have one side exposed to the hydraulic fluid and another, opposite side exposed to the drilling fluid. The piston may have an outer surface adjacent to an inner surface of the sleeve.

The system may comprise a stem that is traversing the piston through a hole in the piston. The hole in the piston may have a surface adjacent to an outer surface of the stem. The surface of the hole may be sized to control a wobble of the stem along a direction perpendicular to a longitudinal axis of the stem. The surface of the hole may further be sized to allow reciprocation of the stem through the hole in the piston.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the embodiments of the disclosure, reference will now be made to the accompanying drawings, wherein:

FIG. 1 is a section view of a known mud pulse telemetry tool that includes a pressure balance system;

FIG. 2 is an exploded view of the pressure balance system shown in FIG. 1; and

FIG. 3 is a sectional view of a system for balancing pressure in a downhole tool in accordance with the disclosure.

DETAILED DESCRIPTION

It is to be understood that the disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Additionally, the exemplary embodiments presented below may be combined in any combination of ways, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure. Finally, all numerical values in this disclosure may be approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, ranges, and proportions disclosed herein or illustrated in the Figures without departing from the intended scope.

The inventors have discovered that the invasion of the chamber filled with hydraulic fluid by the drilling fluid of the known pressure balance system 40 shown in FIG. 2 may be caused by an excessive wobbling amplitude of the piston along a direction perpendicular to the longitudinal axis of the piston and/or of the stem along a direction perpendicular to the longitudinal axis of the stem.

Turning to FIG. 3, a system 140 for balancing pressure in a downhole tool in accordance with the disclosure is illustrated. The pressure balance system 140 may be located in the housing 34 of the tool 10, shown in FIG. 1, instead of the pressure balance system 40.

The pressure balance system 140 includes a piston 144, a cylindrical sleeve 142, a cap 148, a cylindrical stem 136, and a piston stop 139, all of which located inside the pressure housing 34. The piston 144 is positioned inside of the sleeve 142, where it can reciprocate. The piston 144 has an outer surface 110 that is adjacent to an inner surface of the sleeve. A space between the outer diameter of the piston 144 and the inner diameter of the sleeve 142 is sealed using an O-ring 146. The piston 144 has a center hole traversed by the stem 136. The stem 136 can reciprocate in the center hole. The center hole in the piston 144 has a surface 112 that is adjacent to an outer surface of the stem 136. A space between the outer diameter of the stem 136 and the inner diameter of the piston 144 is sealed using a quad seal 156, the illustration of which is schematized. The quad seal 156 is retained in the center hole by a washer 158 and an internal snap ring 160. The cap 148 is located at the bottom end of the sleeve 142. The cap 148 and O-rings 150 are used to create a seal between the sleeve 142 and pressure housing 34. The piston stop 139 is used to stop the piston 44 from coming out of the sleeve 142. The piston 144 is designed to be exposed to drilling fluid on the upper side, and hydraulic fluid on the lower side. The O-Rings 146, 150, and the quad seal 156 are used to isolate the drilling fluid and the hydraulic fluid from each other.

In some embodiments, the outer surface 110 of the piston 144 may be sized to control a wobble of the piston 144 along a direction perpendicular to a longitudinal axis 114 of the piston 144 and to allow reciprocation of the piston 144 inside the sleeve 142. For example, a diameter of the outer surface 110 of the piston 144 may be sized to control the wobble of the piston 144 and to allow the reciprocation of the piston 144 inside the sleeve 142. The diameter of the outer surface 110 may be determined by routine experimentation. The diameter of the outer surface 110 is preferably not so large as to hinder the reciprocation of the piston 144 inside the sleeve 142. The diameter of the outer surface 110 is preferably not so small as to cause premature wear and invasion of section 120, which is filled with hydraulic fluid, by the drilling fluid present in section 122. Optionally, the diameter of the outer surface 110 of the piston may be sized within a first predetermined tolerance, and a diameter of the inner surface of the sleeve 142 may be sized within a second predetermined tolerance. Alternatively or additionally, an axial length of the outer surface 110 of the piston 144 may be sized to control the wobble of the piston 144 and to allow the reciprocation of the piston 144 inside the sleeve 142. The axial length of the outer surface 110 may also be determined by routine experimentation. The length of the outer surface 110 is preferably not so large as to hinder the reciprocation of the piston 144 inside the sleeve 142. The length of the outer surface 110 is preferably not so small as to cause premature wear and invasion of section 120 filled with hydraulic fluid by the drilling fluid present in section 122.

In some embodiments, the surface 112 of the hole may be sized to control a wobble of the stem 136 along a direction perpendicular to a longitudinal axis 116 of the stem 136 and to allow reciprocation of the stem 136 through the hole in the piston. For example, an axial length of the surface 112 of the hole may be sized to control the wobble of the stem 136 and to allow the reciprocation of the stem through the hole in the piston. The axial length of the surface 112 of the hole may be determined by routine experimentation. The surface 112 of the hole is preferably not so large as to hinder the reciprocation of the piston 144 inside the sleeve 142. The surface 112 of the hole is preferably not so small as to cause premature wear and invasion of section 120 filled with hydraulic fluid by the drilling fluid present in section 122.

In order to prepare the pressure balance system 140 for operation, hydraulic fluid is placed inside of the chamber of the pressure balance system 140 in section 120. When the hydraulic fluid fills the chamber, the piston 144 moves upward until it reaches the piston stop 39. A vacuum may then be pulled in the chamber to remove any excess air bubbles. The chamber may then be re-filled again with hydraulic fluid.

Once the chamber of the pressure balance system 140 has been successfully filled, the piston 144 is moved downward and positioned at a predetermined distance from the piston stop 139. During this downward movement, the excess hydraulic fluid exits out of the chamber. The chamber is then sealed off with a plug, securing the hydraulic fluid inside. This positioning of the piston 144 allows the piston 144 to move within the sleeve 142 in response to the downhole pressure of the drilling fluid and heat expansion of the hydraulic fluid.

The claimed invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and description. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the claims to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the claims. 

What is claimed is:
 1. A system for balancing pressure in a downhole tool between a first section filled with hydraulic fluid and a second section filled with drilling fluid, the system comprising: a sleeve located inside a housing of the downhole tool; a piston located inside the sleeve, the piston having one side exposed to the hydraulic fluid and another, opposite side exposed to the drilling fluid; and a stem traversing the piston, wherein the piston has an outer surface adjacent to an inner surface of the sleeve, the outer surface of the piston being sized to control a wobble of the piston along a direction perpendicular to a longitudinal axis of the piston and to allow reciprocation of the piston inside the sleeve.
 2. The system of claim 1, wherein a diameter of the outer surface of the piston is sized to control the wobble of the piston and to allow the reciprocation of the piston inside the sleeve.
 3. The system of claim 2, wherein the diameter of the outer surface of the piston is sized within a first predetermined tolerance.
 4. The system of claim 2, wherein a diameter of the inner surface of the sleeve is sized within a second predetermined tolerance.
 5. The system of claim 1, wherein a length of the outer surface of the piston is sized to control the wobble of the piston and to allow the reciprocation of the piston inside the sleeve.
 6. A system for balancing pressure in a downhole tool between a first section filled with hydraulic fluid and a second section filled with drilling fluid, the system comprising: a sleeve located inside a housing of the downhole tool; a piston located inside the sleeve, the piston having one side exposed to the hydraulic fluid and another, opposite side exposed to the drilling fluid; and a stem traversing the piston through a hole in the piston, wherein the hole in the piston has a surface adjacent to an outer surface of the stem, the surface of the hole being sized to control a wobble of the stem along a direction perpendicular to a longitudinal axis of the stem and to allow reciprocation of the stem through the hole in the piston.
 7. The system of claim 6, wherein a length of the surface of the hole is sized to control the wobble of the stem and to allow the reciprocation of the stem through the hole in the piston.
 8. The system of claim 6, wherein the piston has an outer surface adjacent to an inner surface of the sleeve, the outer surface of the piston being sized to control a wobble of the piston and to allow reciprocation of the piston inside the sleeve.
 9. The system of claim 8, wherein a diameter of the outer surface of the piston is sized to control the wobble of the piston along a direction perpendicular to the longitudinal axis of the piston and to allow the reciprocation of the piston inside the sleeve.
 10. The system of claim 9, wherein the diameter of the outer surface of the piston is sized within a first predetermined tolerance.
 11. The system of claim 9, wherein a diameter of the inner surface of the sleeve is sized within a second predetermined tolerance.
 12. The system of claim 8, wherein a length of the outer surface of the piston is sized to control the wobble of the piston and to allow the reciprocation of the piston inside the sleeve.
 13. A method for balancing pressure in a downhole tool between a first section filled with hydraulic fluid and a second section filled with drilling fluid, the method comprising: providing a sleeve inside a housing of the downhole tool; providing a piston inside the sleeve; providing a stem through a hole in the piston; and filling the first section with hydraulic fluid, wherein the piston has an outer surface adjacent to an inner surface of the sleeve, the outer surface of the piston being sized to control a wobble of the piston along a first direction perpendicular to a longitudinal axis of the piston and to allow reciprocation of the piston inside the sleeve, and wherein the hole in the piston has a surface adjacent to an outer surface of the stem, the surface of the hole being sized to control a wobble of the stem along a second direction perpendicular to a longitudinal axis of the stem and to allow reciprocation of the stem through the hole in the piston.
 14. The method of claim 13, wherein a diameter of the outer surface of the piston is sized to control the wobble of the piston and to allow the reciprocation of the piston inside the sleeve.
 15. The method of claim 13, wherein a length of the outer surface of the piston is sized to control the wobble of the piston and to allow the reciprocation of the piston inside the sleeve.
 16. The method of claim 13, wherein a length of the surface of the hole is sized to control the wobble of the stem and to allow the reciprocation of the stem through the hole in the piston. 